1. Field of the Invention
The present invention relates to a method of simultaneously establishing the call connection among multi-users using a virtual sound field and a computer-readable recording medium for implementing the same, and more particularly to such a method of simultaneously establishing the call connection among multi-users using a virtual sound field, in which when a plurality of users simultaneously make a video-telephone call to each other they can feel as if they conversed with each other in a real-space environment, and a computer-readable recording medium for implementing the same.
2. Background of the Related Art
A portable terminal is increasing in number owing to its convenience of communication between end users irrespective of time and place. Along with the technological development of such a portable terminal, there has been the advent of an era enabling from the exchange of voice and data to further transmission and reception of video data during a telephone call. In addition, it is possible to establish a video-telephone call between multi-users as well as a one-to-one video-telephone call.
During such a video-telephone call among the multi-users, all the voices of multi-speakers in a conversation are heard on a one-dimensional direction regardless of the positions of the speakers whose image signals are transmitted. Also, in case where multiple speakers simultaneously converse with one another, voices of the multiple speakers are heard at once so that there frequently occurs a case where it is difficult to discern which speaker talks about which subject.
If a person talks with strangers during a video-telephone call, there occurs a case not capable of discerning which speaker talks about which subject due to their unfamiliar voices to thereby result in any confusion.
In case of a video-telephone call using a portable terminal or a computer, if voices of speakers are heard as if they talked to each other in a real-space environment, such confusion will be reduced. However, it is impossible to implement reality of conversation like in a real-space environment during a video-telephone call according to the prior art.
The core mechanism of recognizing the source location of the human voice is a head related transfer function (HRTF). If head related transfer functions (HRTFs) for the entire region of a three-dimensional space are measured to construct a database according to the locations of sound sources, it is possible to reproduce a three-dimensional virtual sound field based on the database.
The head related transfer function (HRTF) means a transfer function between a sound pressure emitted from the sound source in a arbitrary location and a sound pressure at the eardrums of human beings. The value of the HRTF varies depending on azimuth and elevation angle.
In case where the HRTF is measured depending on azimuth and elevation angle, when a sound source which is desired to be heard at a specific location is multiplied by an HRTF in a frequency domain, an effect can be obtained in which the sound source is heard at a specific angle. A technology employing this effect is a 3D sound rendering technology.
A theoretical head related transfer function (HRTF) refers to a transfer function H2 between a sound pressure Psource of the sound source and a sound pressure Pt at the eardrum of human being, and can be expressed by the following Equation 1:
                              H          2                =                                            p              t                                      p              source                                .                                    [                  Equation          ⁢                                          ⁢          1                ]            
However, in order to find the above transfer function, the sound pressure Psource of the sound source must be measured, which is not easy in an actual measurement. A transfer function H1 between a sound pressure Psource of the sound source and a sound pressure Pff at a central point of the human head in a free field condition can be expressed by the following Equation 2:
                              H          1                =                                            p              ff                                      p              source                                .                                    [                  Equation          ⁢                                          ⁢          2                ]            
Using the above Equations 1 and 2, a head related transfer function (HRTF) can be expressed by the following Equation 3:
                    H        =                                            H              2                                      H              1                                =                                    p              t                                      p              ff                                                          [                  Equation          ⁢                                          ⁢          3                ]            
As in the above Equation 3, the sound pressure Pff at a central point of the human head in a free field condition and the sound pressure Pt at the eardrum of human being are measured to obtain a transfer function between the sound pressure at a central point of the human head and the sound pressure on the surface of the human head, and then a head related transfer function (HRTF) is generally found by a distance correction corresponding to the distance of the sound source.